FULL PRODUCT VERSION :
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) Client VM (build 25.131-b11, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
ver 7, Windows 7 Enterprise

A DESCRIPTION OF THE PROBLEM :
While calling the java.lang.String.valueOf(Object) method with null value the method returns "null" which is a string value. Method returns as return (obj == null) ? "null" : obj.toString(); Here "null" is a string and which makes the handling of returned value difficult as user remains unsure wheather a value was passed or not.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Call String.valueOf(null);

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
null or exception
ACTUAL -
"null" (a String value) which is a character array.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class StringProblem {
    public StringProblem() {
super();
    }

    public static void main(String[] args) {
//initially when value is null
String checkNull = null;
String stringNull = String.valueOf(checkNull); // performing existing valueOf of function on null value

System.out.println("Value at stringNull variable is :" +stringNull+": Performing string operation->result :"+
stringNull.charAt(0));
// this line should give runtime exception i.e. NullPointerException as checkNull is null,
// valueOf(Object) returned "null" but it should return null
// and performing any string operation will give NullPointerException.
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
    public static String valueOf(Object obj) {
        return (obj == null) ? null : obj.toString();
    }

// when object is null, value returned should be null rather "null".

SUPPORT :
YES